A more detailed inspection of the contagion process in the ordered homogeneous states shows that it develops spatial dynamics that cannot be described by simple percolation or mixing approximations.
In particular, in this regime the agents are known to display superdiffusive displacements perpendicular to the mean heading [1]}, [2]}, which will result in a faster propagation of the infection along this direction.
Starting from a localized outbreak, we thus observe the rapid initial formation of a band-like infected region perpendicular to the mean agent orientation, which is then advected by the mean flow, as shown in Fig.REF .
This type of contagion process was identified in all our simulations of states OH-1 and OH-2; we expect it to also be present in any ordered homogeneous state of self-propelled particles with similar dynamics.
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